[google-appengine] Re: Problems with Geohash / Inaccuracy / ow to deal with this ?

Thu, 04 Sep 2008 12:09:04 -0700

Pierre a écrit : 
Yep Adam, you're right.
Turning into string seems to turn false to true. Good point but it
doesn't solve my troubles completely.

I try to copy paste some code and output to show you some weird
things.

Regards,

Pierre

On 4 sep, 19:31, Adam <[EMAIL PROTECTED]> wrote:
  
Should you be using:

   str(hashPoi) > str(hashSW)

or Geostring instead?

A

On Sep 4, 6:59 am, Pierre <[EMAIL PROTECTED]> wrote:

    
Hi,
      
Here's an example :
[GCC 4.1.3 20070929 (prerelease) (Ubuntu 4.1.2-16ubuntu2)] on linux2
Type "help", "copyright", "credits" or "license" for more information.>>> import geohash
      
hashSW = geohash.Geohash((1.5765380859375,42.894076403348976))
hashNE = geohash.Geohash((6.1907958984375,44.3002644115815))
hashPoi = geohash.Geohash((3.867915,43.733638))
hashPoi > hashSW
            
False
      
hashPoi < hashNE
            
True
      
With geoIndex :>>> hashSW = geohash.Geoindex((1.5765380859375,42.894076403348976))
      
hashNE = geohash.Geoindex((6.1907958984375,44.3002644115815))
hashPoi = geohash.Geoindex((3.867915,43.733638))
hashPoi > hashSW
            
False
      
hashPoi < hashNE
            
True
      
I might be missing something but I thought : hash(SW) < hashPoi <
hash(NE)
      
How do you use it and do you find something different ?
      
Regards,
      
Pierre
      
On 4 sep, 12:33, Ubaldo Huerta <[EMAIL PROTECTED]> wrote:
      
Do you have a example of a point whose geohash value isn't greater
than SW, NE geohashes?
        
I've tried, in  the python interpreter, many examples, and haven't
observed what you're describing. It's pretty scary because I'm writing
a lot of code for a geo app that's based on that property of
geohashes, described athttp://labs.metacarta.com/blog/27.entry/,
working. I knew about equator, etc cases needed special handling, but
I'm not too concerned.
        
-U
        
On Sep 3, 10:23 pm, Pierre <[EMAIL PROTECTED]> wrote:
        
Hi,
          
I need to find points (lat/lng) within a certain bounding box. To do
so, I tried Geohash python implementation (http://mappinghacks.com/
code/geohash.py.txt).
          
Problem's data is :
- I have 2 points (South west SW corner / North east NE corner)
describing a geographic Bounding box
- I have a model (let's call it 'Poi') having a field "geohash" of
type Db.StringProperty + Lat and Lng field (Float)
          
Question is : How on earth (lol :-) ) can I find all Poi within my
bounding box ?
          
I've already tried something like :
          
Create Geohash for SW, create Geohash for NE and do something like :
          
"SELECT * FROM Poi WHERE geohash >:1 and geohash <= :2, geohash(SW),
geohash(NE)"
          
Also tried with geoindex, at different depth but all this fails and
still give points not located within Bounding box.
Also tried like describe in "http://labs.metacarta.com/blog/27.entry/
geographic-queries-on-google-app-engine/" to create a small
surrounding box for each Poi and then create a geohash for this
specific bounding box to be in between my SW->NE bounding box....
          
Nothing is working even with "not worst case" (I mean equatorial
problem...) case/
          
Any help will be greatly appreciated.
          
Thanks all,
          
Pierre
Here is some code + corresponding output, you will see that it retrieves a point located outside bbox :

geoHash1 = geohash.Geohash((float(point[1]), float(point[0])))
geoHash2 = geohash.Geohash((float(point[3]), float(point[2])))
logging.info(" SW : "+str(point[0])+" "+str(point[1])+"\n\t\t"+str(geoHash1))
logging.info(" NE : "+str(point[2])+" "+ str(point[3])+"\n\t\t"+str(geoHash2))
pois = db.GqlQuery("Select * from Poi WHERE geoHash >:1 and geoHash <:2",str(geoHash1),str(geoHash2))
pois1 = Poi.all()
logging.info("Points already in the datastore : ")
for poi in pois1:
   logging.info(" Geohash poi "+poi.geoHash+" poiKey : "+str(poi.key())+" lat : "+str(poi.lat)+" Lng : "+str(poi.lng)+" ")
   logging.info("-------------------------------------------------------")

logging.info("Points for the given Bbox : ("+str(point[0])+","+str(point[1])+")->("+str(point[2])+" "+ str(point[3])+")")
if pois.count() != 0:
  for poi in pois:
     logging.info(poi.geoHash+" poiKey : "+str(poi.key())+" lat : "+str(poi.lat)+" lng : "+str(poi.lng))


************************************************************************************
And now, let's have a look at some output when draging map around and trying to see if point disapear both from screen and from query result when out of the (SW, NE) bbox :

INFO:root: SW : 43.26720631662829 4.61151123046875
                speq0uw18pb50
INFO:root: NE : 44.18220395771566 8.12713623046875
                spvg2gn5bpb08
INFO:root:Points already in the datastore :
INFO:root: Geohash poi spfb018s0yn6w poiKey : ag9hbmFseXRpY3NtYXNodXByCQsSA1BvaRgBDA lat : 43.602709 Lng : 3.867915
INFO:root:-------------------------------------------------------
INFO:root:Points for the given Bbox : (43.26720631662829,4.61151123046875)->(44.18220395771566 8.12713623046875)
INFO:root:spfb018s0yn6w poiKey : ag9hbmFseXRpY3NtYXNodXByCQsSA1BvaRgBDA lat : 43.602709 lng : 3.867915

*********************
Clearly : the unique point should be OUTSIDE the bbox thus not return in output "Points for the given Bbox". So, Am I doing something wrong either with datastore / GQL or geohash ?

Thanks.

Pierre


--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups "Google App Engine" group.
To post to this group, send email to [email protected]
To unsubscribe from this group, send email to [EMAIL PROTECTED]
For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en
-~----------~----~----~----~------~----~------~--~---

Reply via email to